The invention relates generally to direct gasoline-injected internal combustion engines, and more particularly, to reducing soot formation and improving running quality of such engines.
Known internal combustion engines include a cylinder block having a crankcase. In a v-type engine, two banks of cylinders extend radially from the crankcase. Each cylinder bank in a v-type six cylinder engine, for example, has three cylinders. In addition, and in a direct gasoline injected engine, gasoline is injected directly into each cylinder.
The direct burning of gasoline droplets in a cylinder causes soot formation due to burning unvaporized gasoline in the cylinder, and poorer fuel-air mixture formation as compared to a homogenous charge engine. At idle speeds, soot formation and mixture formation are not significant because the injected fuel quantities are small as compared to the injected quantities at higher speeds, and because the gasoline droplets are small due to later injection timing into higher cylinder pressures. As the injection timing becomes earlier and fueling rates increase to a maximum rate just before the transition from stratified combustion to homogenous combustion, soot formation and mixture formation adversely impact engine operation.
Known engines typically are operated with a step jump in injection timing to avoid substantial soot generation and improve mixture formation. Particularly, at a predetermined engine RPM, a small movement in the throttle causes a step increase, rather than a smooth increase, in the engine RPM. The step increase in RPM provides that the engine converts from stratified combustion to homogeneous combustion with very little throttle movement, which facilitates reducing heavy soot formation and improves mixture formation.
In marine engines, although such a step increase engine RPM avoids heavy soot production and improves mixture formation, the step increase in engine RPM results in a potentially objectionable increase or decrease in boat speed with very little throttle movement. It would be desirable to provide methods and apparatus for engine operation so that heavy soot production is avoided yet allows smooth engine acceleration and deceleration without significant engine RPM increases and decreases with small throttle movements.